This invention relates to processes and apparatus for the recovery of metals from phosphate flue dust.
The flue dusts typically are generated from the elemental phosphorous industry which processes phosphate rock to product phosphorous. Phosphate ore is crushed, mixed with a source of carbon, and introduced into electrical furnaces operating at high temperatures. The phosphate is reduced to elemental phosphorous and distilled from the furnace along with other volatile constituents in a gas stream. The phosphorous is condensed from this gas stream, with remaining metals in the gas stream being scrubbed in Cottrell electrostatic precipitators. This precipitator dust, now known as flue dust, contains precious metals, base metals and phosphates. This flue dust is the starting material for the process of the subject invention.
The metals contained in the precipitator dust, including arsenic and cadmium, and especially silver, do not respond to conventional hydrometalurgical or pyrometallurgical recovery schemes, with a maximum recovery of silver in the order of 25-35%. However, after the precipitator dust is processed pursuant to the teachings of the subject invention, metals readily respond and the recovery is substantially improved.